Ba, IN PPM 
>1000 1000-500 500-210 2I0-I05 
105-60 60-30 
SEDIMENT-SIZE CLASSES, IN pm 
STATION 5-2 
M4=X—— 
MI0-O—— 
30-10 lO-I 
FIGURE 12B.—Concentrations of barium in different size fractions of bottom sediments collected on cruises 4 and 10 at site- 
specific station 5-2 on Georges Bank. 
diameter and centered on station 5. Inclusion of 
areas to the east of station 5, particularly in light 
of the small increases in Ba measured during the 
third year at stations 2 and 3, would increase the 
percentage of drilling-related Ba accounted for in 
the sediments. 
We conclude that the barite from drilling mud is 
associated with the fine-sediment fraction in low 
concentration and is widely distributed. 
The overall results of this study have important 
implications in predicting the fate and effects of any 
contaminants discharged on Georges Bank, which 
have an affinity for sediments or suspended par- 
ticulates. For those contaminants that are rendered 
harmless by dilution, the tidal and storm currents 
are sufficient to disperse material over 
wide areas. Benthic organisms can assist in dis- 
persing a contaminant that is added to the sea floor 
to deeper horizons in the sediments. These pro- 
cesses act quickly; half of the barite inventory at 
26 
the station 5 drill site was removed from the 0- to 
2-cm sediment layer in 0.34 year. For those con- 
taminants known to be dangerous or potentially 
dangerous at any concentration, or for those con- 
taminants that are added in excess of the system’s 
capacity to dilute, the same energetic processes of 
dispersion will endanger a wide area of the bank. 
SUMMARY OF IMPORTANT FINDINGS 
1. Barium (present in barite, a major constituent 
of drilling mud) has increased by a factor of 5.9 
in bulk (unfractionated) sediments 200 m from 
the drill site in block 410 as a result of drilling. 
The maximum barium concentration (172 ppm) 
was within the range of predrilling concentra- 
tions (28-300 ppm) measured at other sampling 
stations of this program. Because of the low tox- 
icity of barium in the form of barite (BaSO,), 
